I wonder if the person who designed the cover for this book can tell the difference between a chromatic and a diatonic harmonica. The artwork features very prominently a diatonic harmonica (10 reed Marine Band model). The book however exclusively deals with maintenance and tweaking of the chromatic model.
So, if you are a chromatic player, get this book. It will give you complete descriptions of all the parts of the harmonica and how to maintain them.
You will also find a couple of playing and tweaking tips.
Diatonic users should better get a book like "Creative Blues Harp: Diatonic Harmonica" by Harris J. Foghorn or "The Complete Harmonica Method: Diatonic" by Bobby Joe Holman.